This invention relates to a through-hole wiring board.
As a process for forming an electroconductive circuit on a printed wiring board, there is a process in which as described in xe2x80x9cDenshi Zairyoxe2x80x9d for October, pp. 42-46 (1994), an electroconductive circuit is formed by using a paste obtained by mixing electroconductive powder such as gold, silver, copper, carbon optionally additives. In fields where a high electroconductivity is required, gold powder or silver powder has been generally used.
An electroconductive paste containing silver powder is used for forming the wiring layers (the electroconductive layers) of printed wiring boards, electronic parts and the like, or the electric circuits and electrodes of electronic parts because of its good electroconductivity. Such a paste, however, is disadvantageous in that when an electric field is applied thereto in a high-temperature and high-humid atmosphere, silver electrodeposition called migration occurs on the electric circuits or the electrodes, so that a short circuit is produced between the electrodes or wirings. Several measures for preventing the migration have been adopted. Measures such as the application of a moistureproof coating material on the surface of a conductor or the addition of a corrosion inhibitor (e.g. a nitrogen-containing compound) to the electroconductive paste have been investigated but have been not sufficiently effective.
The present invention is intended to provide a through-hole wiring board which is free from the defects of the above-mentioned prior art, permits easy formation of an electrical connection of through-holes, has a high reliability on connection, and has a small thickness of an electroconductive material formed on copper foil lands.
The present invention provides a through-hole wiring board comprising through-holes passing through a substrate and filled with an electroconductive material; copper foil lands and copper foil circuits formed on surfaces of the substrate; insulating layers formed on the copper foil circuits and between necessary portions of the copper foil lands and the copper foil circuits; and printed circuits (jumper circuits) formed by another electroconductive material having a different composition from that filling the through-holes on a part of the copper foil circuits, and the copper foil lands and the insulating layers except for unnecessary portions for electroconductivity; wherein the printed circuits and ends of the through-holes are electrically connected with an electroconductive material having a different composition from that filling the through-holes.